1. Field of the Invention
The present invention relates to a device for controlling light sources which are used in an optical fixing unit of a thermal printer, or used for lighting in a copying machine, a scanner and so forth, or used for optical recording.
2. Description of the Related Art
For example, a color thermal printer uses a color thermosensitive recording paper in which cyan, magenta and yellow thermosensitive coloring layers are formed on a support member in order. In such a printer, the recording paper is pressed and heated by a thermal head to record a color image in the thermosensitive coloring layers. The yellow and magenta thermosensitive coloring layers are respectively fixed, just after recording, by applying ultraviolet rays having a peculiar wave-length range relative to each coloring layer. The ultraviolet rays are emitted from an optical fixing unit, a light source of which is an ultraviolet lamp being a kind of a fluorescent lamp. As for a copying machine, a scanner or the like, an original is illuminated by a fluorescent lamp and so forth being as a light source. In such machines, obtained transmission light or reflection light is photoelectrically converted to store an image in a recording medium as image data.
Some of the above-mentioned optical fixing units and scanners have a plurality of light sources for purposes of increasing an application amount of the ultraviolet rays and a light amount of the illumination. These light sources simultaneously apply the ultraviolet rays or simultaneously illuminate the original. For example, in a color thermal printer, ultraviolet lamps for applying the ultraviolet rays having an identical wave length are arranged in a conveying direction of the color thermosensitive recording paper so as to constitute a single optical fixing unit. The respective ultraviolet lamps are energized by letting a current flow. On the other hand, there is a color thermal printer of a three-head one-pass system in which images of the respective colors are recorded by three thermal heads. In such a printer, positions for applying the ultraviolet rays to a color thermosensitive recording paper are different. However, the respective ultraviolet lamps for fixing the yellow and magenta thermosensitive coloring layers are simultaneously energized by letting the current flow.
By the way, when the currents simultaneously flow in a plurality of the light sources, for example N (integer) fluorescent lamps, the N-times currents flow in comparison with a case in that a single light source is employed. Thus, it is necessary to increase a rated power of a power circuit for supplying the power to the light sources. This causes a problem in that the power circuit needs to be enlarged. Meanwhile, when an inverter circuit or the like is used for letting the intermittent current flow and for repeatedly energizing the fluorescent lamps, peaks and troughs of the current flowing in the respective fluorescent lamps overlap with each other. In other words, a range of a load change becomes wide on the power circuit so that a voltage outputted from the power circuit is made unstable. Due to this, sometimes, a bad effect is given to the other operation in which the power circuit is used in common.